Several transmission line and antenna arrangements compatible with printed circuit embodiment of microwave electronic apparatus are known in the electronic arts and have found application in radar, satellite communication and other present day systems. In these systems a transmission line realized in the form of printed circuit conductors is often used to communicate radio frequency energy to or form an antenna element.
The printed circuit conductor in these embodiments may for example be arranged in the form of what is known as "stripline", an arrangement wherein a strip conductor is received between two adjacent ground planes, or alternately in the form of "microstrip" line wherein a single conductor is spaced from a single ground plane. The printed circuit conductor may also be in the form of "slot" line wherein a slot formed in one planar conductor is spaced from a second ground plane conductor. Another common arrangement for such printed circuit transmission line is known as coplanar waveguide line and is in the form of an electrically isolated signal conductor bounded laterally by adjacent ground plane conductors in a coplanar disposition.
Some of these transmission line types have also been used in configurations wherein an apparent part of one or more transmission line elements also functions as an active element portion of an antenna, an antenna coupled to the transmission line. In these arrangements the transmission line and antenna element portions may appear structurally integral however for functional and analysis purposes a segregation of functions is convenient. This combination of transmission line and antenna functions in single structure has been achieved particularly in the case of microstrip transmission lines. Unlike the case of such microstrip antennas there appears to be little reporting in the technical literature concerning wide strip coplanar waveguide lines or open ended discontinuities and their radiating properties, areas of consideration in the present invention.
This latter transmission line disposition which has been identified by the name of "coplanar waveguide" offers several advantages including its easy layout and fabrication by single layer photographic techniques and acceptable electrical losses. The ease with which coplanar transmission line of this nature can be coupled to resonators and antenna elements is also significant and approaches the topic of interest in the present invention. Perhaps the most convenient of antenna arrangements usable with coplanar waveguide transmission line is the antenna known as a "patch" antenna. Literally such antennas may consist of a printed circuit conductor area of selected and resonance-based physical size disposed at the terminal point or other selected node along a radio frequency conductor. When used with the above identified microstrip form of printed circuit transmission lines for example the patch antenna is found to be attended by several problems; the primary of which is a limited bandwidth capability. This patch antenna bandwidth often extends over only a few percent of the antenna's design frequency and gives rise to difficulty in spread spectrum communications or multiple systems use applications of the antenna. The present invention in which the patch antenna is improved-upon by combining it with a selected additional form of antenna while yet remaining in the convenient and desirable coplanar waveguide environment is believed to provide a desirable addition to the family of antennas usable in printed circuit microwave apparatus.